As a best practice, we recommend you deploy your image builder and fleet instances in private subnets. This means each fleet instance will access the internet via a corresponding NAT gateway. Each NAT gateway has an elastic IP address that doesn't change.
AppStream 2.0 is non-persistent. After the session is ended, the underlying instance is terminated. I don't recommend editing network interfaces, as that is not a scalable solution.
can you see the nic in ec2 network interfaces page, if so it's worth reserving an elastic ip and trying to bind it outside of appStream if the image builder natively doesn't support static IP
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